Spot welding holders commonly employ multiple electrodes, each fixed in position. Some electrodes apply more pressure on the workpiece than other electrodes because of variations in workpiece thickness and electrode wear. The electrodes function best when they apply equal pressure on the workpiece, splitting the current evenly between the tips. Uneven tip pressure reduces the life of the electrodes.
Conventional practice is to file the inner ends of the electrode shanks to balance the tip pressure on the workpiece. This time-consuming process requires taking the holder apart to file the electrodes and then assembling the holder to determine whether the electrode pressure is even.
Typically, a conventional holder requires maintenance after processing 2,000 pieces.
Some holders are known for balancing the pressure applied by the electrode tips by some type of self-adjusting mechanism. See for example U.S. Pat. No. 2,979,599, issued to Robert B. Width, Apr. 11, 1961, for "Multiple Electrode Holder", and U.S. Pat. No. 3,558,848, issued to Robert B. Width, Jan. 26, 1971, for "Electric Resistance Welding Electrode Holder Three Electrodes in Balanced Force Contact".